Steam generators

ABSTRACT

A steam generator which is particularly adapted to be used in nuclear power plants. A casing is provided with an inlet and outlet to receive and discharge a primary heating fluid from which heat is to be extracted. A pair of tube plates extend across the interior of the casing at the region of the inlet and outlet thereof, and a plurality of tubes extend along the interior of the casing and are connected in parallel between the tube plates with all of the tubes having open ends communicating with the inlet and outlet of the casing so that the primary heating fluid will flow through the interior of the tubes while a fluid in the casing at the exterior of the tubes will extract heat from the primary fluid. The casing has between the tubes at the region of the inlet a superheating chamber and at the region of the outlet a preheating chamber and between the latter chambers an evaporating chamber, the casing receiving water through an inlet at the preheating chamber and discharging superheated steam through an outlet at the superheating chamber. A separator communicates with the evaporating chamber to receive a mixture of steam and water therefrom for separating the steam from the water and for delivering the separated steam to the superheating chamber.

United States Patent [191 Beckmann et al.

[ 5] Dec.2, 1975 I 54 l STEAM GENERATORS [73] Assignee: Waagner-Biro Aktiengesellschaft,

Austria 221 Filed: Nov. 15,1973

211 Appl.No.:416,272

[30] Foreign Application Priority Data Nov. 16, 1972 Austria 9733/72 [52] US. Cl. 122/34; 122/483 [51] Int. Cl. F221) 1/06 [58] Field of Search 122/32, 33, 34, 483; 165/1 12 [56] References Cited UNITED STATES PATENTS 2,845,906 8/1958 Gram, .lr 122/34 2,904,013 9/1959 Davies ct al. 122/32 3,141,445 7/1964 Bell 122/34 3,329,129 7/1967 Sandri.... 122/34 3,380,649 4/1968 Roberts 165/112 3,807,365 4/1974 Lyman ct al 122/32 FOREIGN PATENTS OR APPLICATIONS 1,086,243 10/1967 United Kingdom 122/34 Primary Examinerl(enneth W. Sprague Attorney, Agent, or FirmSteinberg & Blake [57] ABSTRACT A steam generator which is particularly adapted to be used in nuclear power plants. A casing is provided with an inlet and outlet to receive and discharge a primary heating fluid from which heat is to be extracted. A pair of tube plates extend across the interior of the casing at the region of the inlet and outlet thereof, and a plurality of tubes extend along the interior of the casing and are connected in parallel between the tube plates with all of the tubes having open ends communicating with the inlet and outlet of the casing so that the primary heating fluid will flow through the interior of the tubes while a fluid in the casing at the exterior of the tubes will extract heat from the primary fluid. The casing has between the tubes at the region of the inlet a superheating chamber and at the region of the outlet a preheating chamber and between the latter chambers an evaporating chamber, the casing receiving water through an inlet at the preheating chamber and discharging superheated steam through an outlet at the superheating chamber. A separator communicates with the evaporating chamber to receive a mixture of steam and water therefrom for separating the steam from the water and for delivering the separated steam to the superheating chamber.

18 Claims, 12 Drawing Figures US. Patent Dec. 2, 1975 Sheet 1 of2 3,923,008

US. Patent Dec. 2, 1975 Sheet 2 of2 3,923,008

STEAM GENERATORS BACKGROUND OF THE INVENTION The present invention relates to steam generators.

In particular, the present invention relates to steam generators which are suitable for use with nuclear power plants.

The present invention relates especially to a steam generator where steam is generated at the exterior of tubes through which a primary heating fluid flows.

Steam generators of this latter type are known where the tubes are of a U-shaped configuration and connected to a single tube plate. This type of construction has a serious drawback in that the single tube plate must be relatively large so that, particularly with large steam generating units, special manufacturing operations are required for the manufacture of the tube plate. As a result the construction of such steam generators is difficult to carry out.

In addition, the ends of the tubes are welded to the single tube plate, creating thermal stresses which as a result of the size of the components cannot be eliminated by annealing, for example, so that in the finished construction a considerable amount of residual thermal stresses remain. During operation these residual stresses which remain have unfavorable effects.

A further disadvantage encountered in conventional steam generators of the above type is that they cannot accommodate a built-in superheater. As a result the steam which is generated can only be used in a relatively uneconomical manner in special turbines capable of operating with saturated steam.

SUMMARY OF THE INVENTION It is accordingly a primary object of the present invention to provide steam generators which will avoid the above drawbacks.

In particular, it is an object of the present invention to provide a steam generator of the above general type which does not utilize a single tube plate, so that the problems encountered with this conventional feature are avoided.

Thus it is an object of the present invention to provide a steam generator whose components will not have residual thermal stresses which can cause problems during operation of the generator.

Furthermore it is an object of the present invention to provide a steam generator of the above type which can accommodate, as a built-in part of the steam generator, a superheating chamber enabling the steam generator to provide as its output superheated steam which can be efficiently utilized for driving turbines.

It is furthermore an object of the present invention to provide a steam generator which will take advantage of the natural flow of fluids due to thermal and pressure conditions, so as to provide a desired circulation without necessitating the use of pumps and the power required to operate such structures.

In addition it is an object of the present invention to provide steam generators capable of effectively handling the treated fluids in such a way that an exceedingly efficient operation is achieved, providing superheated steam in a highly economical manner.

Furthermore, it is an object of the present invention to provide not only single steam generator units but also multiple steam generator units, with these multiple 2 units using in common certain structures such as a separator for separating steam from water.

According to the invention the steam generator which is particularly suited for use in a nuclear power plant includes a casing means having an inlet and an outlet for respectively receiving and discharging a primary heating fluid from which heat is to be extracted. A pair of tube plates extend across the interior of the casing means at the region of its inlet and outlet, and a plurality of tubes extend along the interior of the casing means, these tubes being connected in parallel between the tube plates and all of the tubes having open ends communicating with the inlet and outlet of the casing means so that the primary heating fluid flows along the interior of the tubes from the inlet to the outlet of the casing means while a fluid at the exterior of the tubes in the casing means extracts heat from the primary fluid. This casing means has between the tube plates at the region of the inlet a superheating chamber and at the region of the outlet a preheating chamber and between the latter chambers an evaporating chamber. The casing means has between the tube plates at the region of the outlet an inlet means for introducing water to be received in the preheating chamber and in the region of the inlet and outlet means for discharging superheated steam from the superheating chamber. A separator means communicates with the evaporating chamber for receiving a mixture of steam and water therefrom and for separating the steam from the water, the separating means communicating with the superheating chamber for delivering to the latter the steam which has been separated from the water.

BRIEF DESCRIPTION OF DRAWINGS The invention is illustrated by way of example in the accompanying drawings which form part of this application and in which:

FIG. 1 is a sectional elevation schematically illustrating one embodiment of a steam generator according to the invention;

FIG. 1A is a transverse section taken along line 1A1A of FIG. 1 in the direction of the arrows and showing in greater detail the structure at the lower part of FIG. 1;

FIG. 1B is a schematic sectional plan view taken along line 18-18 of FIG. 1 in the direction of the arrows and showing how part of the communication is made between the casing of the steam generator and a separator means;

FIG. 2 is a schematic partly sectional elevation of a further embodiment of a steam generator according to the invention;

FIG. 3 is a partly sectional schematic elevation of a further embodiment of a steam generator according to the invention, the section of FIG. 3 being taken along line III-III of FIG. 4 in the direction of the arrows;

FIG. 4 is a schematic sectional plan view of the structure of FIG. 3 taken along line IVIV of FIG. 3 in the direction of the arrows;

FIG. 4A is a schematic partly sectional plan view taken along line 4A-4A of FIG. 3 in the direction of the arrows;

FIG. 4B is a fragmentary partly sectional schematic elevation taken along line 4B-4B of FIG. 4A in the direction of the arrows;

FIG. 5 is a schematic partly sectional elevation of a further embodiment of a steam generator according to the invention;

FIG. 6 is a sectional plan taken along line VI-VI of FIG. 5 in the direction of the arrows;

FIG. 6A is a sectional plan taken along line 6A6A of FIG. 5 in the direction of the arrows; and

FIG. 6B is a fragmentary schematic plan view taken along line 6B-6B of FIG. 5 in the direction of the arrows.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings, FIG. 1 shows a heat exchanger in elevation, this heat exchanger having a bundle of tubes 1 of substantially U-shaped configuration provided with a pair of legs or branches l5 and 16, the branch of the plurality of tubes 1 being shown at the left in FIG. 1 while the branch 16 is shown at the right in FIG. 1. The top ends of the tubes of the branch 15 are fixed with an tube plate 2 while the top ends of the tubes of the branch 16 are fixed with an inlet tube plate 4. The plurality of tubes 1 and the tube plates 2 and 4 are situated in the interior of a casing means 9 which has an inlet 24a for the primary heating fluid and an outlet 24b for the primary heating fluid. Thus, the open ends of all of the tubes communicate with the inlet 24a and the outlet 2412 so that the primary heating fluid flows from the inlet 24a along the interior of the plurality of tubes 1 to the outlet 24b.

The casing means 9 forms in its interior between the tube plates 2 and 4 and at an outlet end region where outlet tube plate 2 is located a preheating chamber 3 one end of which is formed by outlet tube plate 2 and in which water received in the pre-heating chamber 3 through the water inlet means 19 is heated at the exterior of the tubes 1. At the region of the tube plate 2, at the side of the inlet means 19 opposite from the tube plate 2 the casing means 9 carries a baffle means 8 in the form of a metal sheet, for example, through which the tubes extend except for the tubes shown at the right of the branch 15 in FIG. 1. This baffle means 8 serves to place the water introduced by the inlet means 9 in engagement with the entire area of the tube plate 2 which is directed inwardly away from the outlet 24b toward the preheating chamber 3. As a result the entire inner surface of the tube plate 2 is washed with the incoming water so that in this way it is not possible for deposits to become situated at the region of the tube plate 2, and in addition depositions of high salt concentration cannot form. As a result of this washing of the tube plate 2 by the incoming water corrosion is reliably avoided.

The preheating chamber 3 is separated from the remainder of the interior of the casing means 9 by a baffle 26, and between the baffle 26 and the baffle 8 there is an additional baffle 3a. Thus, the water entering through the inlet means 9 is compelled to flow first around the right edge of the baffle 8 and then around the left edge of the baffle 3a, as viewed in FIG. 1, before reaching the space between the baffles 3a and 26.

A conduit 12 has its upper left end, as viewed in FIG. 1, communicating with the space between the baffles 3a and 26 so that all of the preheated water is received in the conduit 12. This conduit 12 extends from the preheating chamber downwardly along the interior of separator means 7 with the conduit 12 having a lower nozzle outlet forming from the incoming preheated water a jet so that in this way an ejector means 13 is formed as illustrated in FIG. 1.

The jet of the ejector means 13 acts to suck water downwardly from the interior of the separator means 7 in a manner described in greater detail below.

The separator means 7 includes a housing situated between the vertically extending branches of the casing means 9 in the manner shown in FIG. 1B. At its lower end this housing communicates with a return conduit 14 through which separated water is delivered to a ringshaped header 18 (FIG. 1A) which surrounds the lower curved portion of the casing means and communicates with the interior thereof through openings 20. In this way water which is separated from steam in the separator means 7 is returned to the interior of the casing means 9.

As a result of this construction the water which is delivered in this way into the interior of the casing means reaches an evaporating chamber 6 therein, and the water is uniformly divided through the above structure between the pair of evaporating chamber portions which extend upwardly along the branches of the easing 9 from the lower curved part thereof. Because this water becomes heated through heat extracted through the tubes 1 from the primary heating fluid therein, the water rises upwardly along both parts of the evaporating chamber 6, so that parallel evaporating actions take place in the pair of vertically extending parts of the evaporating chamber 6 while a series operation takes place with respect to the primary heating fluid in the parts of the evaporating chamber 6 inasmuch as the primary heating fluid first flows downwardly through the tubes 1 and the branch 16 and then upwardly through the tubes 1 in the branch 15. Thus, in the right part of the evaporating chamber 6 in FIG. 1 the water is treated in countercurrent to the primary heating medium while in the left part the water is treated while flowing concurrently with the primary heating medium in the interior of the tubes.

Thus, the water rises in opposition to the force of gravity as a result of the thermal action in the evaporating chamber 6, and as a result of the heat extracted from the primary heating medium the water is converted to steam so that the evaporating chamber 6 includes a steam space 11 as well as a water space 10. The steam space 11 is filled essentially with a foamy mixture of water and steam.

A second baffle 26 separates a superheating chamber 5 from the steam space 11 of the evaporating chamber 6. Thus, this second baffle 26 also extends completely across the interior of the casing means 9, and the superheating chamber 5 has its opposite ends formed respectively by this second baffle 26 and the inlet tube plate 4. Just below the pair of baffles 26 the casing means 9 communicates with a pair of conduits 21 which communicate tangentially with the housing of the separator means 7, so that in this way the mixture of steam and water flows from the evaporating chamber 6 into the separator means 7 which acts as a cyclone in which the mixture of water and steam whirl about the ejector pipe 12 as illustrated in FIG. 1.

As a result of the action which takes place in the separator means 7 dry steam is separated from the water with the latter being sucked downwardly by the jet of the ejector means 13 in the manner described above, and thus the preheated water which forms the jet and the separated water taken from the evaporator chamber 6 are returned to the lower part of the casing 9 as described above.

The dry separated steam flows up to the top of the housing of the separator means 7 to be received in the top open end of a conduit 22 whose lower right end delivers the dry steam to the superheating chamber 5 above the right baffle 26, as viewed in FIG. 1. Thus the superheating chamber 5 is situated between the right baffle 26 of FIG. 1 and the tube plate 4 with the dry steam which is taken from the separator means 7 being superheated by the hot primary heating fluid introduced through the inlet 24a. This incoming dry steam is guided around baffles as illustrated in FIG. 1 in the superheating chamber 5. An outlet means 23 communicates with the upper right region of the superheating chamber 5 to discharge the superheated steam to a predetermined location where use is made of this steam. For example the superheated steam may be used to drive turbines.

Thus, with the steam generator of FIG. 1 the primary heating medium enters the casing means 9 through the inlet 24a and is distributed among the several tubes 1 which are connected with the tube plate 4. The relatively hot primary heating medium flows first through the superheating chamber 5 of the steam generator and then through the evaporating chamber 6. In the preheating chamber 3 the primary heating medium is further cooled. Thus, by providing the preheating chamber 3 the temperature differential is improved so that either the secondary pressure can be increased or the area of the heating surfaces can be reduced.

Referring now to FIG. 2, there is illustrated therein a further embodiment of a heat exchanger of the invention where although the casing means and the tubes are also of a U-shaped configuration, in this embodiment the casing means and the tubes have legs of different lengths with the right leg being shorter, as viewed in FIG. 2. With this construction it is the upper part of the right leg which forms the preheating chamber 3 which extends up to the lower curved portion of the casing means and tubes. Thus, the preheating chamber 3 can extend throughout the length of the right leg of the steam generator and around through the curved portion thereof up to the evaporating chamber 6 which extends along the interior of the casing means which accommodates the longer branch of the curved tubes 1. The lower curved part of the casing means receives the separated waer which is returned from the separator means 7 in the manner described above in connection with FIG. 1. However, in this case the tube 14 for returning the separated water from the separator means 7 communicates directly with the casing means in the manner illustrated in FIG. 2 and a ring-shaped header 18 is not used. Moreover, the water introduced by the inlet means 19 into the preheating chamber 3 flows directly from the latter to the lower part of the steam generator to combine with the water returned through the conduit 14, and then all of this water rises up through the evaporating chamber 6 to be converted into steam, with the steam and water mixture being received in the separator means 7 through a conduit 21 from the top end of the chamber 6 just beneath the baffle 26, as illustrated in FIG. 2. Thus in the embodiment of FIG. 2 circulation takes place only as a result of the heating action.

Above the baffle 26 in FIG. 2 is located the superheating chamber 5 with the inlet of the casing means 9 being situated above the tube plate 4 which forms the top end of the superheating chamber 5 with the embodiment of FIG. 2. Thus, through the conduit 21,

which communicates tangentially with the cyclonetype of separator means 7 in FIG. 2, the mixture of steam and water is subjected to a cyclone action in the separator means 7, with the separated water returning through the conduit 14 to the evaporating chamber 6 while the dry separated steam flows out of the separator means 7 through the conduit 22 shown in FIG. 2 in order to enter into the lower right part of the superheating chamber 5 in the manner illustrated in FIG. 2. From the upper left part of the superheating chamber 5 the superheated steam discharges in order to be received where use will be made of the superheated steam. It will be noted that in both of the embodiments of FIGS. 1 and 2 the separator means 7 is located at the exterior of the casing means 9. Moreover it is clear that comments made above with respect to the embodiment of FIG. 1 are equally applicable to that of FIG. 2.

FIG. 3 illustrates a further embodiment of a steam generator or heat exchanger according to the invention. With this embodiment the tubes are straight throughout their entire length, as contrasted with the curved tubes of the embodiments of FIGS. 1 and '2. However, with the embodiment of FIG. 3 the outer casing means 9 also has a top inlet 24a through which the primary heating medium enters to be received in the top open ends of the several tubes 1 which are connected with the tube plate 4 which extends across the interior of the casing means 9 as illustrated in FIG. 3. The primary heating medium flows downwardly along the hollow interior of the tubes 1 to be received at the outlet 24b of the casing means 9, a second tube plate 2 being fixed to the interior of the casing means 9 extending across the interior of the casing means 9 and fixed with the lower ends of the tubes 1 all of which have their open ends in communication with the outlet 24b.

Between the plates 2 and 4 the interior of the casing means 9 of the embodiment of FIG. 3 forms the preheating chamber 3, located just above the tube plate 2, while above the preheating chamber 3 is located the evaporating chamber 6 which in turn is separated by the baffle 26 from the superheating chamber 5 located at the uppermost part of the steam generator and extending from the baffle 26 up to the tube plate 4. Thus, in this case the inlet means 19 will deliver the water into the interior of the preheating chamber 3 with this water also serving to wash the surface of the tube plate 2 which is directed toward the preheating chamber 3. From the preheating chamber 3 the water flows around suitable baffles to reach the evaporating chamber 6, and in this case the mixture of steam and water is received by a separator means 7 accommodated in the interior of the casing means 9 as described below with the dry steam flowing from the separator means 7 through suitable openings in the battle 26 into the superheating chamber 5 from which the steam is discharged by the outlet means 23. Thus, with the embodiment of FIG. 3 the fluid heated at the exterior of the tubes 1 flows primarily in countercurrent to the primary heating medium.

As the mixture of steam and water reaches the top end of the evaporating chamber 6, this mixture is deflected by the baffle 26 radially outward through approximately to the separator means 7 which in this embodiment surrounds the tubes 1 in the interior of the casing means 9. The baffle 26 is formed with openings 22 (FIGS. 4 and 4A), and these openings communicate only with the separator means 7. Thus from the inner edges of the openings 22 wall portions 22a extend downwardly from the baffle 26 along the exterior of the tubes 1. These walls 22a are fixed with radially extending separator walls 22b, the outer curved edges of which are fixed directly with the inner surface of the casing 9. The walls 22b are formed with elongated tapered openings 22c which at their top ends communicate with the lower surface of curved baffles 22d. These curved baffles extend between the adjoining walls 22b at the spaces covered by the baffle 26, so that the mixture of steam and water is compelled to flow around the baffles 22d and then downwardly between the radial walls 22b. These baffles 22d form curved extensions of a cylindrical wall 22e which surrounds the tubes 1, which is spaced inwardly of the casing 9 and which includes the wall portions 22a. Thus, the radial walls 22b define with the cylindrical wall 222 elongated channels 14 through which water will return downwardly toward the lower end of the evaporating chamber 6. On the other hand, as the mixture of steam and water flow outwardly and downwardly beyond the outer edge of the curved baffles 22d, the dry steam flows first laterally through the openings 22c and then upwardly between the upper portions of the walls 22b and the openings 22 of the baffle 26 into the superheating chamber 5. In this way the separator means of FIG. 3 forms a phase separator separating the water from the steam with the dry steam flowing up into the superheating chamber 5 while the separated water returns to the lower end of the evaporating chamber 6 in the manner illustrated in FIG. 3. Thus, through the centrifugal action achieved with the separator means 7 of the embodiment of FIG. 3 the steam and water are separated from each other to respectively flow upwardly and downwardly as described above. The radial walls 22b define elongated return channels 14 for returning the separated water.

The upper end of the preheating chamber 3 is defined by a transverse baffle formed with a narrow outlet 17 for the preheated water, this narrow outlet 17 forming a nozzle which directs the preheated water in the form of a jet upwardly along the interior of the evaporated chamber 6. In this way the jet also forms an ejector-type of construction serving to suck the separated water flowing down through the channels 14 up into the evaporating chamber 6.

The structure is shown in FIG. 3 at the left half in section and at the right half in elevation with part of the casing means removed. Thus the section line IIIIII of FIG. 4 illustrates the manner in which the structure is illustrated in FIG. 3. In order to improve the illustration the separator means 7 is illustrated in FIG. 4 in accordance with the section line IVIV of FIG. 3. Furthermore, it is apparent from FIG. 4 that the separator means includes, for example, six open regions uniformly distributed about the axis of the steam generator and through which the mixture of steam and water is radially deflected outwardly through approximately 90, with the dry steam flowing up in the spaces between the spaces where the mixture of steam and water is deflected down into the separator means.

FIG. 5 illustrates a construction according to which the tubes 1 are divided into groups of tubes 24 and 25 which have different lengths. The group of tubes 24 is shorter than the group 25 and forms in its entirety only parts of the preheating and evaporating surfaces, while the group of tubes 25 form the remainder of the preheating and' evaporating surfaces as well as the entire superheater structure together with the casing means. In order to separate the heating surfaces on one side of the U-shaped tubes, namely the left side as shown in FIG. 5, the groups 24 and 25 are separated by the elongated channel 14 which is of rectangular configuration and which serves to return the separated water to the evaporating chamber. Thus, with this construction, the hot primary heating medium entering through the inlet 24a just below the tube plate 4, to which the lower left ends of all of the tubes are connected as illustrated in FIG. 5, is divided into a pair of separate upwardly flowing streams with the right part of the stream flowing upwardly through the group of tubes 24 on the right side of the channel 14, as viewed in FIG. 5, while the left part of the stream of primary heating medium flows upwardly through the group of tubes25 situated on the left side of the channel 14, as viewed in FIG. 5. Thus, the part of the primary heating medium which is received in the group of tubes 24 forms an evaporating medium while the part which flows upwardly through the tubes 25 at the left of the channel 14 forms the superheating medium. Therefore, with the embodiment of FIG. 5 the superheating chamber is located only at the left of the channel 14 in the left downwardly extending tubular portion of the casing means 9, this casing means 9 having an upper spherical portion accommodating the upper curved ends of the groups of tubes 24 and 25. Of course with the embodiment of FIG. 5 the tube plates 2 and 4 are situated beneath the bundle of tubes and the curved portions of the tubes are located at the highest parts thereof.

Thus it will be seen that the right tubular part of the casing means 9 in FIG. 5 accommodates both groups of tubes 24 and 25 with both groups in this right elongated tubular portion of the casing 9 forming part of the preheating chamber which extends upwardly from the lower tube plate 2 to the evaporating chamber which is situated at the region of the upper curved part of the group of tubes 24. An inlet means 19 is provided just above the tube plate 2 for introducing the water which as a result of the heat in the casing means rises upwardly, with the water separated from the steam being delivered by the channel 14 to the left branch of the group of tubes 24 in the manner described above so that evaporation action of the incoming water from the inlet means 19 takes place at the right part of the generator, as viewed in FIG. 5 in parallel with the evaporation of the water separated from the steam and received from the return channel 14. In this way parallel evaporation takes place in the two legs of the casing means 9 illustrated in FIG. 5, with the mixture of steam and water flowing up to be received in the hollow interior of a tapered or conical pressure enclosure means 7a which forms the lower part of the separator means 7 of FIG. 5.

The separator means 7 is housed within the upper spherical part of the casing means 9 from which the two tubular branches illustrates in FIG. 5 extend downwardly, and the pressure chamber in the spherical upper part of the casing means 9 is situated around the cyclone type of separator means 7 and accommodates only the upper portion of the group of tubes 25. In this way the pressure is reliably maintained as required in the corresponding tubular part of the casing means 9.

The mixture of steam and water received in the interior of the tapered housing 7a flows up to the top thereof to be received in the cyclone separator part of the separator means 7 as illustrated in FIG. 6A. Thus the mixture of steam and water is received at the upper central part of the tapered housing 7a which communicates with a spiral passage 7b from which the whirling mixture of steam and water is delivered into a cylindrical housing 70 having openings in its bottom wall through which water can flow back down through the channel 14 while steam flows up through the open top of the cylindrical enclosure 7c to reach the interior of the upper spherical portion of the casing means 9 where the upper U-shaped portion of the group of tubes 25 is located.

It will be noted that part of the interior of the enclosure 70 communicates through an opening 7d with a hollow tapered tubular component 7e which has a top open end above the top end of the enclosure 7c so that dry steam can also enter through the opening 7d in order to flow through the interior of the tubular extension 7e into the hollow interior of the upper spherical part of the casing means 9. Thus, the dry steam will reach the hollow interior of the upper spherical part of the casing means 9 where it will be noted only the upper part of the group of tubes 25 is located so that only the dry steam will be superheated by flowing downwardly along the group of tubes 25 at the left of the conduit 14, as viewed in FIG. 5. The group of tubes 25 are completely separated from the group of tubes 24 by the tapered lower housing part 7a, with the right part of the group of tubes 25 passing through suitable openings in an extension of the lower part of the tapered housing portion 7a, as shown in FIG. 5.

The above-described structure of FIG. lends itself to an assembly of steam generator units including all of the above structure except that all of the steam generator units can cooperate with a common separator means 7. Such an arrangement is illustrated in FIG. 6 which is taken along line VIVI of FIg. 5 in the direction of the arrows. Thus, considering the horizontal central line of FIG. 6 it will be seen that below this horizontal central line one of the units as described above and shown in FIG. 5 is located while above this central line is located a second steam-generating unit. In both cases the uppermost inlet walls of the rectangular channels 14 extend over the enclosure 7c in the manner shown in FIG. 68, so that a unit as described above and shown in FIG. 5 is duplicated to the rear of the central vertical plane of the entire assembly except that the groups of tubes 24 and 25 are reversed right-to-left. Thus in this case the lower tapered enclosure 7a will be situated over the upper U-shaped portions of both of the groups of tubes 24 in the manner described above.

Although the two units which cooperate with the common separator means are shown above and below the horizontal central line in FIG. 6, it is also possible to provide an arrangement where each unit extends diagonally across the central axis of the entire assembly so that at the upper right portion of FIG. 6 would be located an arrangement as shown at the lower right portion of FIG. 6 and the structure shown at the upper right quadrant of FIG. 6 could be located at the lower right quadrant of FIG. 6. Thus, such an arrangement also is possible with the groups of tubes having their U- shaped curved top ends extending diagonally across the hollow interior of the sphe rical upper part of the casing means 9. With these constructions the shorter group of tubes 24 also will form the evaporating surfaces while the longer groups of tubes form part of the evaporating surfaces as well as preheating and superheating surfaces.

What is claimed is:

1. In a steam generator, particularly adapted for nuclear power plants, casing means having an inlet end region and an outlet end region respectively having an inlet'and outlet for respectively receiving and discharging a primary heating fluid from which heat is to be extracted, said end regions being separate and spaced from each other, inlet and outlet tube plates extending across the interior of said casing means in said inlet and outlet end regions thereof, respectively, and a plurality of tubes extending along the interior of said casing means, said tubes being connected in parallel between said tube plates and all of said tubes having open ends communicating with said inlet and outlet of said casing means so that the primary heating fluid flows along the interior of said tubes from said inlet end region to said outlet end region of said casing means while a fluid at the exterior of said tubes in said casing means extracts heat from the primary fluid, said casing means having between said tube plates in said inlet end region a superheating chamber one end of which is formed only by said inlet tube plate and in said outlet end region a preheating chamber one end of which is formed only by said outlet tube plate and chambers an evaporating chamber in series with said preheating chamber, said preheating chamber being spaced from and out of communication with said inlet end region and said inlet tube plate as well as the portions of said tubes connected to said inlet tube plate, and said casing means having between said tube plates at said outlet end region an inlet means for introducing water to be received in said preheating chamber and at said inlet end region an outlet means for discharging superheated steam from said superheating chamber, and separator means communicating with said evaporating chamber for receiving a mixture of steam and water therefrom and for separating the steam from the water, said separator means having a steam discharge communicating directly with said superheating chamber for delivering to the latter the steam separated from the water to be superheated only while flowing in said superheating chamber to said outlet means.

2. The combination of claim 1 and wherein said tubes are of a substantially U-shaped configuration.

3. The combination of claim 1 and wherein a baffle means is situated in said preheating chamber adjacent said inlet means for directing water against the tube plate at the outlet region of said casing means for washing said tube plate substantially over the entire area thereof which is directed inwardly toward said preheating chamber.

4. The combination of claim 1 and wherein said evaporating chamber includes a steam space and a water space, respectively adjacent said superheating chamber and said preheating chamber, and said separator means communicating both with said steam space and said water space for respectively receiving steam and water therefrom.

5. The combination of claim 4 and wherein said separator means is a cyclone situated at the exterior of said casing means and including conduits which communicate with said water space and steam space for receiving the water and steam therefrom, respectively.

6. The combination of claim 1 and wherein said separator means communicates also with said evaporating chamber of said casing means for returning to said evaporating chamber water separated from the steam and water received by said separator means, and ejector means communicating with said preheating chamber for receiving the water delivered thereto by said inlet means and for delivering the latter water in the form of a jet through a part of said separator means which communicates with said evaporating chamber to return water thereto separated from the steam and water mixture, so that said ejector means will utilize the water which is preheated in said preheating chamber to suck water separated from the steam at said separator means and deliver the latter water together with the water received from said preheating chamber under pressure to said evaporating chamber.

7. The combination of claim 1 and wherein a nozzle means is situated between said preheating chamber and evaporating chamber for directing the water received in said preheating chamber from said inlet means in the form of a jet from said preheating chamber into said evaporating chamber, and said separator means communicating with said evaporating chamber at the region of said preheating chamber for returning to said evaporating chamber adjacent said preheating chamber water separated from the mixture of water and steam, so that the latter water which is returned from said separator means to said evaporating chamber will be acted upon by the jet of water issuing from said preheating chamber to be directed with the water from the preheating chamber along the interior of said evaporating chamber.

8. The combination of claim 1 and wherein said casing means and tubes therein have a substantially U- shaped configuration provided with an intermediate curved portion and on opposite sides thereof elongated portions of different lengths, the shorter of said elongated portions of said tubes in casing means forming said preheating chamber with said outlet of said casing means being situated at the shorter portion thereof while the longer portion of said tubes and easing means forms the evaporating and superheating chambers.

9. The combination of claim 1 and wherein said tubes have a U-shaped configuration and have on opposite sides of an intermediate curved portion elongated portions both of which form parts of said evaporating chamber, and the parts of said tubes which form said parts of said evaporating chamber being connected in series for directing the primary heating fluid sequentially along the interior of said tubes first through one of said parts of said evaporating chamber and then through the other of said parts of said evaporating chamber, while the interior of said casing means which surrounds said tubes at said parts of said evaporating chamber defines spaces in which the fluid at the exterior of the tubes is treated in parallel at said parts of said evaporating chamber.

10. The combination of claim 1 and wherein said tubes are of a U-shaped configuration and include at least some tubes which have an intermediate curved portion situated in said evaporating chamber of said casing means, and said separator means being situated over the latter curved portion of the latter tubes.

11. The combination of claim and wherein said casing means includes a spherical pressure enclosure in which said separator means is located and said casing means having parallel tubular extensions in which legs of said tubes of U-shaped configuration are located.

12. The combination of claim 1 and wherein said casing means has a plurality of inlets and outlets for receiving and discharging the primary heating fluid and houses in its interior a plurality of sets of said tubes to form therewith a plurality of steam-generating units,

12 and said separator means being common to and communicating with all of the latter units.

13. In a steam generator, particularly adapted for nuclear power plants, casing means having an inlet and outlet for respectively receiving and discharging a primary heating fluid from which heat is to be extracted, a pair of tube plates extending across the interior of said casing means at the region of said inlet and outlet thereof, and a plurality of tubes extending along the interior of said casing means, said tubes being connected in parallel between said tube plates and all of said tubes having open ends communicating with said inlet and outlet of said casing means so that the primary heating fluid flows along the interior of said tubes from said inlet to said outlet of said casing means while a fluid at the exterior of said tubes in said casing means extracts heat from the primary fluid, said casing means having between said tube plates at the region of said inlet a superheating chamber and at the region of said outlet a preheating chamber and between the latter chambers an evaporating chamber, and said casing means having between said tube plates at the region of said outlet an inlet means for introducing water to be received in said preheating chamber and in the region of said inlet an outlet means for discharging superheated steam from said superheating chamber, and separator means communicating with said evaporating chamber for receiving a mixture of steam and water therefrom and for separating the steam from the water, said separator means communicating with said superheating chamber for delivering to the latter the steam separated from the water, said casing means and said tubes therein being of a substantially U-shaped configuration having an intermediate curved portion, a ring-shaped header surrounding said curved portion of said casing means and communicating through said casing means with the interior thereof where the curved portion of said tubes is located, and said separator means communicating with said header for returning to the latter water separated from the steam and water mixture so that from said header the separated water is delivered from the separator means back to the evaporating chamber.

14. The combination of claim 1 and wherein said tubes include two groups of tubes both of which are of U-shaped configuration with one of said groups being longer than the other and including said superheating chamber for generating superheated steam with the latter flowing in countercurrent to the direction of flow of the primary heating fluid in the tubes which extend along said superheating chamber.

15. The combination of claim 1 and wherein said separator means is situated in said casing means and surrounds said evaporating chamber, and baffle means separating said separator means from said superheating chamber, said baffle means cooperating with said separator means for deflecting steam and water from said evaporating chamber outwardly through an angle of approximately from said tubes into said separator means and the latter directing separated water downwardly along the exterior of said tubes at said evaporating chamber while said separator means communicates through said baffle means with said superheating chamber to direct separated steam through said baffle means into said superheating chamber, so that said separator means acts as a phase separator for separating liquid from steam prior to flow of the latter into said superheating chamber.

14 the side of said inlet means opposite from said outlet tube plate, .and said second baffle forming the end of said preheating chamber opposite from said outlet tube plate 18. The combination of claim 12 and wherein said casing means has a substantially spherical housing portion common to all of said units and housing said separator means. 

1. In a steam generator, particularly adapted for nuclear power plants, casing means having an inlet end region and an outlet end region respectively having an inlet and outlet for respectively receiving and discharging a primary heating fluid from which heat is to be extracted, said end regions being separate and spaced from each other, inlet and outlet tube plates extending across the interior of said casing means in said inlet and outlet end regions thereof, respectively, and a plurality of tubes extending along the interior of said casing means, said tubes being connected in parallel between said tube plates and all of said tubes having open ends communicating with said inlet and outlet of said casing means so that the primary heating fluid flows along the interior of said tubes from said inlet end region to said outlet end region of said casing means while a fluid at the exterior of said tubes in said casing means extracts heat from the primary fluid, said casing means having between said tube plates in said inlet end region a superheating chamber one end of which is formed only by said inlet tube plate and in said outlet end region a preheating chamber one end of which is formed only by said outlet tube plate and chambers an evaporating chamber in series with said preheating chamber, said preheating chamber being spaced from and out of communication with said inlet end region and said inlet tube plate as well as the portions of said tubes connected to said inlet tube plate, and said casing means having between said tube plates at said outlet end region an inlet means for introducing water to be received in said preheating chamber and at said inlet end region an outlet means for discharging superheated steam from said superheating chamber, and separator means communicating with said evaporating chamber for receiving a mixture of steam and water therefrom and for separating the steam from the water, said separator means having a steam discharge communicating directly with said superheating chamber for delivering to the latter the steam separated from the water to be superheated only while flowing in said superheating chamber to said outlet means.
 2. The combination of claim 1 and wherein said tubes are of a substantially U-shaped configuration.
 3. The combination of claim 1 and wherein a baffle means is situated in said preheating chamber adjacent said inlet means for directing water against the tube plate at the outlet region of said casinG means for washing said tube plate substantially over the entire area thereof which is directed inwardly toward said preheating chamber.
 4. The combination of claim 1 and wherein said evaporating chamber includes a steam space and a water space, respectively adjacent said superheating chamber and said preheating chamber, and said separator means communicating both with said steam space and said water space for respectively receiving steam and water therefrom.
 5. The combination of claim 4 and wherein said separator means is a cyclone situated at the exterior of said casing means and including conduits which communicate with said water space and steam space for receiving the water and steam therefrom, respectively.
 6. The combination of claim 1 and wherein said separator means communicates also with said evaporating chamber of said casing means for returning to said 95 evaporating chamber water separated from the steam and water received by said separator means, and ejector means communicating with said preheating chamber for receiving the water delivered thereto by said inlet means and for delivering the latter water in the form of a jet through a part of said separator means which communicates with said evaporating chamber to return water thereto separated from the steam and water mixture, so that said ejector means will utilize the water which is preheated in said preheating chamber to suck water separated from the steam at said separator means and deliver the latter water together with the water received from said preheating chamber under pressure to said evaporating chamber.
 7. The combination of claim 1 and wherein a nozzle means is situated between said preheating chamber and evaporating chamber for directing the water received in said preheating chamber from said inlet means in the form of a jet from said preheating chamber into said evaporating chamber, and said separator means communicating with said evaporating chamber at the region of said preheating chamber for returning to said evaporating chamber adjacent said preheating chamber water separated from the mixture of water and steam, so that the latter water which is returned from said separator means to said evaporating chamber will be acted upon by the jet of water issuing from said preheating chamber to be directed with the water from the preheating chamber along the interior of said evaporating chamber.
 8. The combination of claim 1 and wherein said casing means and tubes therein have a substantially U-shaped configuration provided with an intermediate curved portion and on opposite sides thereof elongated portions of different lengths, the shorter of said elongated portions of said tubes in casing means forming said preheating chamber with said outlet of said casing means being situated at the shorter portion thereof while the longer portion of said tubes and casing means forms the evaporating and superheating chambers.
 9. The combination of claim 1 and wherein said tubes have a U-shaped configuration and have on opposite sides of an intermediate curved portion elongated portions both of which form parts of said evaporating chamber, and the parts of said tubes which form said parts of said evaporating chamber being connected in series for directing the primary heating fluid sequentially along the interior of said tubes first through one of said parts of said evaporating chamber and then through the other of said parts of said evaporating chamber, while the interior of said casing means which surrounds said tubes at said parts of said evaporating chamber defines spaces in which the fluid at the exterior of the tubes is treated in parallel at said parts of said evaporating chamber.
 10. The combination of claim 1 and wherein said tubes are of a U-shaped configuration and include at least some tubes which have an intermediate curved portion situated in said evaporating chamber of said casing means, and said separator means being situated over the latter curved portion of the latter tubEs.
 11. The combination of claim 10 and wherein said casing means includes a spherical pressure enclosure in which said separator means is located and said casing means having parallel tubular extensions in which legs of said tubes of U-shaped configuration are located.
 12. The combination of claim 1 and wherein said casing means has a plurality of inlets and outlets for receiving and discharging the primary heating fluid and houses in its interior a plurality of sets of said tubes to form therewith a plurality of steam-generating units, and said separator means being common to and communicating with all of the latter units.
 13. In a steam generator, particularly adapted for nuclear power plants, casing means having an inlet and outlet for respectively receiving and discharging a primary heating fluid from which heat is to be extracted, a pair of tube plates extending across the interior of said casing means at the region of said inlet and outlet thereof, and a plurality of tubes extending along the interior of said casing means, said tubes being connected in parallel between said tube plates and all of said tubes having open ends communicating with said inlet and outlet of said casing means so that the primary heating fluid flows along the interior of said tubes from said inlet to said outlet of said casing means while a fluid at the exterior of said tubes in said casing means extracts heat from the primary fluid, said casing means having between said tube plates at the region of said inlet a superheating chamber and at the region of said outlet a preheating chamber and between the latter chambers an evaporating chamber, and said casing means having between said tube plates at the region of said outlet an inlet means for introducing water to be received in said preheating chamber and in the region of said inlet an outlet means for discharging superheated steam from said superheating chamber, and separator means communicating with said evaporating chamber for receiving a mixture of steam and water therefrom and for separating the steam from the water, said separator means communicating with said superheating chamber for delivering to the latter the steam separated from the water, said casing means and said tubes therein being of a substantially U-shaped configuration having an intermediate curved portion, a ring-shaped header surrounding said curved portion of said casing means and communicating through said casing means with the interior thereof where the curved portion of said tubes is located, and said separator means communicating with said header for returning to the latter water separated from the steam and water mixture so that from said header the separated water is delivered from the separator means back to the evaporating chamber.
 14. The combination of claim 1 and wherein said tubes include two groups of tubes both of which are of U-shaped configuration with one of said groups being longer than the other and including said superheating chamber for generating superheated steam with the latter flowing in countercurrent to the direction of flow of the primary heating fluid in the tubes which extend along said superheating chamber.
 15. The combination of claim 1 and wherein said separator means is situated in said casing means and surrounds said evaporating chamber, and baffle means separating said separator means from said superheating chamber, said baffle means cooperating with said separator means for deflecting steam and water from said evaporating chamber outwardly through an angle of approximately 90* from said tubes into said separator means and the latter directing separated water downwardly along the exterior of said tubes at said evaporating chamber while said separator means communicates through said baffle means with said superheating chamber to direct separated steam through said baffle means into said superheating chamber, so that said separator means acts as a phase separator for separating liquid from steam prior To flow of the latter into said superheating chamber.
 16. The combination of claim 1 and wherein a baffle extends completely across the interior of said casing means at said inlet end region thereof at the side of said outlet means opposite from said inlet tube plate, and said baffle forming the end of said superheating chamber opposite from said inlet tube plate.
 17. The combination of claim 16 and wherein a second baffle extends completely across the interior of said casing means in said outlet end region thereof at the side of said inlet means opposite from said outlet tube plate, and said second baffle forming the end of said preheating chamber opposite from said outlet tube plate.
 18. The combination of claim 12 and wherein said casing means has a substantially spherical housing portion common to all of said units and housing said separator means. 